1. Field of the Invention
This invention relates to a contact-type image sensor that can be used in a facsimile apparatus, a device for the reading of letters and images, and the like.
2. Description of the Prior Art
As sensors for the reading of images, reduction-type image sensors such as CCD sensors and MOS sensors have been used. However, because the sensing sections of these reduction-type image sensors are small, about 2-4 cm, the reduction of the manuscript has had to be on the order of 1/5 to 1/10, and for that reason, it has been necessary for the length of the light path from the manuscript to the sensing section to be long. Moreover, as the percentage of the reduction of the manuscript increases, the lens aberration becomes a problem influencing the design accuracy of the optical system upon which the overall performance of the apparatus is dependent.
In recent years, contact-type image sensors have been actively developed by which an image with the same size as the manuscript is formed on the lightreceiving surface of the sensing section with the same length as the width of the manuscript via an optical fiber lens array. As photodetectors that are used in such contact-type image sensors, there are those of a thin film-type with CdSSe thin films, amorphous-Si thin films, or the like, and those of a multiplechip-type in which IC sensors such as CCD sensors, bipolar IC sensors, MOS-type sensors, or the like are arranged in a line in the longitudinal direction so that these multiplechips can give the same length as the width of the manuscript. As a replacement for the optical fiber lens arrays for optical systems, there are optical systems in which a sensing section is disposed on one end of a bundle of optical fibers.
FIG. 5 shows a conventional contact-type image sensor with an optical fiber lens array, wherein a light source a illuminates the manuscript b and the reflected light from the manuscript b passes through the optical fiber lens array c, resulting in an image with the same size as the manuscript on a photodetector p. This contact-type image sensor has the following drawbacks:
(1) The conjugate length of the optical fiber lens array c is about 15-40 mm, and it is necessary to have this conjugate length open between the manuscript b and the photodetector p;
(2) Because the focal depth of the optical fiber array c is shallow, the positional adjustment of each part of this optical system in the process for the manufacture of the said contact-type image sensor is necessary;
(3) When bright optical fiber lenses are used for an optical fiber lens array, the aberration of color becomes a problem, and accordingly in cases where color sensors are used, optical fiber lenses that have a long conjugate length but that are dark must be used; and
(4) The cost of the optical fiber lens array c is high.
FIG. 6 shows a conventional contact-type image sensor with a bundle of optical fibers, wherein a light source e illuminates the manuscript f, and the reflected light from the manuscript passes through the optical fibers h, which are buried in a conductive substrate g, and arrives at a photodetector i that is disposed on one end of the bundle of optical fibers h. This contact-type image sensor has the following drawbacks:
(1) The light-receiving surface of the photodetector i must be brought into contact with the end of the bundle of optical fibers h in order to prevent light rays from the optical fibers from spreading out and overlapping between the adjacent optical fibers;
(2) When the photodetector i is formed directly on the end of the bundle of optical fibers h, the material for the formation of the photodetector i must be thin films, and moreover the cost of the substrate in which the optical fibers h are buried becomes high; and
(3) The number of sensors that can be produced at the same time is limited, which makes the productivity low.